Although California Gov. Gavin Newsom has long been considered a top contender for the Democratic presidential nomination, the focus has now shifted to whether he might be Kamala Harris' running mate after President Biden abruptly suspended his re-election campaign.

As concerns about President Biden's mental acuity and age grew following his poor debate performance against former President Trump in June, Newsom repeatedly denied rumors of running a so-called "shadow campaign," which many speculated he was conducting since his debate with GOP presidential candidate Florida Gov. Ron DeSantis last year.

Now that VP Harris has taken over the Democratic Party ticket's helm and garnered enough support from delegates to become the party's nominee to face off against Trump, many have suggested Newsom could be back in consideration for a spot in the White House.

HARRIS' SHIFT FROM TOUGH-ON-CRIME PROSECUTOR TO SOCIAL JUSTICE ADVOCATE FACES SCRUTINY FROM CONSERVATIVE GROUP

Gavin Newsom campaigns for Biden in Michigan

California Gov. Gavin Newsom campaigns for President Biden July 4, 2024, at a county Democratic Party event in South Haven, Mich.  (Chris duMond/Shutterstock)

But is Newsom really out of the running to be Harris' VP? The 12th Amendment could be a potential hurdle.

Ratified in 1804, it addresses the procedures for electing the president and vice president in response to issues that arose in the country's early elections. It established that electors would cast separate ballots for president and vice president, rather than two votes for president as previously required.

If the president and running mate are from the same state, however, electors from that state cannot cast votes for both offices. This rule ensures that the electors from the home state of the nominees cannot affect the outcome of the election for both positions.

ABORTION, 'FREE' EDUCATION AMONG TOP ISSUES FOR HARRIS VOTERS

Harris rally

Vice President Kamala Harris speaks to supporters during a campaign rally at West Allis Central High School July 23, 2024, in West Allis, Wis. (Jim Vondruska/Stringer)

In the first contested election under the 12th Amendment, Thomas Jefferson and his running mate, Aaron Burr, were from Virginia. The election was ultimately decided by the House of Representatives since the amendment hadn't been ratified yet.

However, there are ways around the statute. In the 2000 presidential election, George W. Bush and his running mate, Dick Cheney, were both residents of Texas, which raised questions at the time about whether they could legally run together.

To navigate the 12th Amendment statute, Cheney, who had been a long-time Texas resident, changed his official residency to Wyoming to comply with the 12th Amendment. The move was made to ensure that the electors from Texas would not be in a position to vote for both candidates.

GOV NEWSOM ORDERS HOMELESS ENCAMPMENTS TORN DOWN ACROSS CALIFORNIA: 'NO MORE EXCUSES'

Harris and Newsom

Presumptive Democratic nominee Kamala Harris has yet to pick her running mate. (Andrew Harnik/Staff)

Harris is reportedly working with a short list of candidates to choose her vice presidential pick in the next two weeks before the Democratic National Convention in Chicago. 

CLICK HERE TO GET THE FOX NEWS APP

Harris’ list of potential running mates, according to NBC News, was whittled down to Arizona Sen. Mark Kelly, Pennsylvania Gov. Josh Shapiro, North Carolina Gov. Roy Cooper, Transportation Secretary Pete Buttigieg, Kentucky Gov. Andy Beshear and Minnesota Gov. Tim Walz.

Newsom endorsed Harris for president Sunday, writing on X that "no one is better to prosecute the case against Donald Trump’s dark vision and guide our country in a healthier direction than America’s Vice President, @KamalaHarris."

Newsom's office pointed Fox News Digital to the governor's X post when reached for comment on his VP chances.

Harris' campaign did not immediately respond to a request for comment.

Fox News Digital's Andrew Mark Miller contributed to this report.